Some general questions for the prius...
#11
Re: Some general questions for the prius...
rolling_drag + ( (coef_of_drag * area) * (velocity**2) )
- rolling_drag - a function of tires, wheel bearings and transmission losses
- coef_of_drag - the coefficient of drag is determined by vehicle shape, air density and Reynolds number
- area - the cross section of the vehicle
- velocity - speed
There is pretty good agreement between various benchmarks and the predicted performance for a warmed-up vehicle. The key is getting the vehicle warmed up, both the ICE and transaxle. But there are other effects that keep us from achieving the maximum: (1) warm-up, (2) braking losses (even with regeneration), (3) critical transaxle transition speeds (42 mph in the Prius) and (4) non-linear ICE efficiency (it gets lossy at higher rpms.)
The Japanese, single tank record also was in the 20-25 mph range thanks to the modest speeds of the commuting route. Even the first Prius marathon used speeds below 40 mph. During the Insight marathon, the average speed was 18 mph and for the last three days, 15 mph. The physics tell us why.
Bob Wilson
Last edited by bwilson4web; 02-08-2007 at 10:52 AM.
#12
Re: Some general questions for the prius...
If only that were really the case... The physics explanation is posted above, but anyone whose ever driven a bicycle knows it's easier to keep a low speed than a high one. The increased momentum is a result of the speed-- the speed is the result of the energy expended by the engine, or in our bicycle example, the cyclist himself.
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